Light diffusers are widely used in lighting devices, for example in luminaires, and allow spreading out or scattering light in a desired manner, to provide a diffused light, for example better adapted to a uniform lighting.
Static and uniform light diffusers are well known, which can be based from diffusing reflectors, or translucent devices for example made with ground glass.
In most applications it can however be desirable that a light diffuser is configured for being easily adaptable, that is: a light diffuser having adjustable light diffusing properties. Such light properties include light diffusion, glare and beam width or full width at half maximum, commonly designated by the acronym FWHM. The ability to adjust all these light properties for a luminaire is highly desirable.
U.S. Pat. No. 8,553,341 B2 relates to an electro-active optical device comprising a deformable polymer film substrate and a rigid optical element, which in one embodiment is a diffusing structure, provided on the substrate. Electrodes are connected to the substrate in order to enable deformation of the substrate, which in turn enables the rigid element to be displaced in the place of the substrate.
Published international patent application WO 2014/013389 relates to a diffuser comprising a partially transparent first layer and an adjoining transparent second layer, the first layer being continuous and comprising a stretchable elastomer, the second layer being a segmented layer comprising a material with a high effective stiffness measured as the product of the thickness of the material and the elastic modulus of the material.
The light diffusers described in the two references above however involve complex hardware structures that are not necessarily easy to design and assemble in production, and further involve active actuators to act on a stretchable structure by means of electrodes. Also, such structures are relatively thick, which makes it difficult to easily integrate them in luminaires without affecting compactness or cosmetic aspect thereof.